On Fri, Jul 3, 2015 at 7:37 AM, Denys Vlasenko <[email protected]> wrote: > On Thu, Jul 2, 2015 at 6:09 PM, Andy Lutomirski <[email protected]> wrote: >> On Thu, Jul 2, 2015 at 5:09 AM, Borislav Petkov <[email protected]> wrote: >>> On Mon, Jun 29, 2015 at 12:33:46PM -0700, Andy Lutomirski wrote: >>>> Signed-off-by: Andy Lutomirski <[email protected]> >>>> --- >>>> arch/x86/entry/entry_64.S | 63 >>>> +++++++++++----------------------------- >>>> arch/x86/entry/entry_64_compat.S | 5 ++++ >>>> 2 files changed, 22 insertions(+), 46 deletions(-) >>>> >>>> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >>>> index ce2c9049abef..08a37ec049f0 100644 >>>> --- a/arch/x86/entry/entry_64.S >>>> +++ b/arch/x86/entry/entry_64.S >>>> @@ -508,7 +508,16 @@ END(irq_entries_start) >>>> >>>> testb $3, CS(%rsp) >>>> jz 1f >>>> + >>>> + /* >>>> + * IRQ from user mode. Switch to kernel gsbase and inform context >>>> + * tracking that we're in kernel mode. >>>> + */ >>>> SWAPGS >>>> +#ifdef CONFIG_CONTEXT_TRACKING >>>> + call enter_from_user_mode >>>> +#endif >>> >>> I think you can make this much cleaner by getting rid of the ifdeffery >>> and pushing it into the enter_from_user_mode() function: >>> >>> __visible void enter_from_user_mode(void) >>> { >>> #ifdef CONFIG_CONTEXT_TRACKING >>> >>> ... >>> >>> #endif >>> } >>> >>> The disadvantage of all that cleanliness is that we get one dumb >>> >>> call enter_from_user_mode >>> >>> there to this abomination: >>> >>> ffffffff810014f0 <enter_from_user_mode>: >>> ffffffff810014f0: e8 db 97 67 00 callq ffffffff8167acd0 >>> <__fentry__> >>> ffffffff810014f5: 55 push %rbp >>> ffffffff810014f6: 48 89 e5 mov %rsp,%rbp >>> ffffffff810014f9: 5d pop %rbp >>> ffffffff810014fa: c3 retq >>> ffffffff810014fb: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) >>> >>> which sux. >>> >>> We sure could use LTO here. >>> >> >> You mean link-time asm optimizations? Turning off frame pointers in >> leaf functions as long as rbp is still preserved might not be so >> terrible either. >> >> I'm torn on this one. In principle, you're right, or we could have a >> macro CALL_ENTER_FROM_USER_MODE that does nothing if context tracking >> is off. OTOH, that's also kind of messy. > > busybox has IF() macros: > > IF_CONTEXT_TRACKING(call enter_from_user_mode) > > Unlike #if, this needs one line, not three.
I predict all of these call sites will get moved to C before 4.3. If not, then I'd be glad to clean this part up. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
